Proposed is a novel method to image early stage cancer cells by targeting upregulated cell surface proteases. One focus will be to image breast cancer tumors using CdSe nanoparticles targeted to a cell surface protease known as MT-SP1, which has been found to have upregulated activity in breast cancer. The design of the tag includes a CdSe fluorophore, a peptide that is specific for targeting MT-SP1, a variable length spacer, and a phosphonate inhibitor to bind the tag to the active site. The second focus is to develop a protease activated high contrast agent by adding FRET capabilities through the addition of Au nanoparticles. These will quench the emission inherent to CdSe, and will be released upon binding to the enzyme. The advantages of these approaches are: 1) the target, which is an active cell surface, highly selective protease that is bound to the membrane, 2) the interchangeable nature of the imaging agent's components, 3) the enhanced emission and lack of photobleaching of the nanoparticle fluorophores compared to currently used fluorophores, and 4) the ability to covalently attach nanoparticles to the target, allowing for localization, stoichiometric labeling, and long term cellular fate studies. [unreadable] [unreadable] [unreadable]